Tanning



Patented Dec. 13, 1938 TANNING John Arthur Wilson, Milwaukee, Wla, assignor to Hall Laboratories; Inc., Pittsburgh, Pa., a corporation or Pennsylvania No Drawing. Application May 17, 1937; Serial No. 143,120

13 Claims. (Cl. 149-5) This invention relates to the manufacture of leather, and more particularly to the; tanning of hides and skins with solutions of an alkali-metal phosphate or the corresponding acids.

This application is a-continuation-in-part of my copending application Serial No. 84,478,.filed June 10, 1936.

For convenience, I will refer mainly to the alkali-metal phosphates, it being understood that the corresponding acids may be employed. The

preferred alkali-metal phosphate which I employ as a tanning agent is Grahams salt, (Textbook ofInorganic Chemistry, edited by J. Newton Friend, vol. 6, part 2, page 177, by J. B. R. Prideaux, Philadelphia, 1934; Gmelin, Handbuch der Anorganischen Chemie, vol. 21, page 922, 8th edition, Berlin, 1928); or Grahams metaphosphate (A Dictionary of Chemistry, by Henry Watts, vol. 4, page 578, New York, 1873; A Treatise on Chemistry, by Roscoe & Schorlemmer, vol. 2, part 1, page 283, New York, 1923). Grahams metaphosphate or salt is believed to consist principally of sodium hexametaphosphate. The sodium hexametaphosphate is assumed to be a complex of the general formula Naz(Na4PsO1a) although some authorities believethat salts of the formula N&5(NaPsO1a) and Na4(NazPaO1a) may also be present. I

v Solutions which are similar to solutions of Grahams salt may be made by dissolving waterinsbluble Maddrell salts or Kurrol salts in acid solution, as described in the co pending application of Casimir J. Munter, Serial No. 68,442, filed March" 12, 1936; When I refer to a solution of a glassy material containing the P03 radical, I intend to include not only a solution of Grahams salt, but also a solution of Kurrol, Maddrell andother water-insoluble alkali-metal phosphates rendered soluble by the addition of acid.

Grahams salt which consists principally of sodium hexametaphosphate, is a glassy (noncrystalline) sodium hexametaphosphate. Sodium trimetaphosphate, on the other hand, is a crystalline material and although having anap- ,45 preciable tanning action, is considerably less eiiective than Grahams salt. In fact,the trimetaphosphate'has only approximately one-third 1 the tanning effect of Grahams salt. Another to P205 of 3:1.

- iiter.

sodium pyrophosphate has been found to have practicallyno tanning efiect onanimal skin.

The materialslwhich I employ as tanning agents in accordance with the present invention have the general formula (M20)a:.\P205)y-, in which M is hydrogen, ammonium and/or an alkali-metal, and in which the molar ratio of M20 to P205 is less than 2:1. In this formula, where M is hydrogen, the material is an acid, and where M is an alkali-rnetal or ammonium, it is a phosphate. Sodium metaphosphate (NaPOa), or sodium hexametaphosphate (NasPcOis) which is known as Grahams salt, have a molar ratio of Nazo to P205 of 1:1. Sodiumtripolyphosphate(NasPaOm) has a molar ratio of NazO to P205 of 5:3. Tetra: sodium pyrophosphate (NarPzOq) has a molar ratio 01 NazO to P205 of 2:1, and trisodium orthophosphate (NasP04) has a molar ratio of NaaO Neither the pyrophosphate nor the orthophosphate has an appreciable "tanning actionon animal skins and do not come within the scope of the present invention. The metaphosphates and tripolyphosphates may be regarded as salts of condensed or molecularly dehydrated phosphoric acids having a greater degree of .molecular dehydration than pyrophosphoric acid. I believe that the glassy alkali-metal phosphates. have. the general formula (NaPoah, in which a: is greater than 3, or Na3PO4(NaPOa), in which a: is greater than 1. I

So far as I am aware, no one has'ever before suspected that phosphates have tanning actions of their own, 'under any conditions. From 1m studies of atomic structure, and chemical combination, I reasoned that complex phosphates of suftlciently high molecular weight should exhibit 'marked'tanning actions on animal hide, particularly when applied in acid solution, and that the rate or degree 01 tanning should increase as the pH value of the solution is lowered, by the addition of acid, to the point where the hide protein acquires a maximum positive electrical charge (about pH=2.4)..

My theory was subjected to a number ocf series of tests which proved the correctness of the reasoning. In one series, 20 gram portions of hide powder were treated for 24 hours with 200 cc. portions of a solution of Graham salt containing phosphate equivalent to 1 mol P205 per This solution had a pH value of 5.65. One portion was used without pH adjustment. To another portion, sodium hydroxide was added to I raise the pH value; to 8.10. To the others, increasing amounts of hydrochloric acid were .Table I pH Value Grams P105 combined with 00 grams Before After tanning tanning hide Drown 8.10 7. 48 0. 04 5. 65 5. 58 0. 3S 5. 00 5. 01 0. 46 3. 98 4. 39 l. 78 2. 97 4. 09 2. 42 2. 01 2.65 a a. s2

Ihis work was followed by a series of practical demonstrations on cowhides, calfskins and goatskins. A typical example follows: After the usual beamhouse operations of soaking, ileshing, liming, unhairing, scudding, washing and bating, the stock was weighed and put into a drum. For each 100 pounds bated weight of stock, there was added 3.75 pounds Graham salt in 12 gallons water at 70 F. plus a sufflcient amount of hydrochloric acid to reduce the initial pH value of the solution to 1.0. The bated stock causes the pH value to rise, but enough more acid wasthen. added to bring the, pH value of the solution to 2.4.. Thestock was run in this liquor, with occasional drumming, for 24 hours, after which the stock was washed and drained and then either fatliquored or swabbed with oil, glycerine, butyl carbitol or other suitable material and dried. The product was a white leather of great strength and durability.

v I then conceived of a modification of the above procedure in order 'to make a soft, white, washable leather; havingsome marked advantages for special uses.

In the above operation, along with the 3.75 pounds of Graham salt, there was added 25 pounds of 40% formaldehyde. After tanning for 24 hours in acid medium, alkali was added gradually to raise the pH. value of the solution slowly to the range 8.0 to 9.0. The stock was then kept in the liquor over night, with occasional drumming. It was then washed, fat-liquored and dried. The product was a pure white, soft, washable leather.

The alkali-metal trimetaphosphates and tripolyphosphates exhibit some tanning action, but are not nearly as effective as Graham's salt. A' comparison of the tanning action of these phosphates with Graham's salt is given in the following table. The tanning time was 24 hours and the pH value of the liquor 3.0.

Table II use.

com w Phosphate used 100 grams hide protein Leather tanned inaccordance with my process is pure white, but may be colored to any desired tint or shade. When fatliquored in the ordinary way, it can be made as soft, pliable and flexiable as desired, or can be so treated as to be very firm and resistant to abrasion. It has a relatively high tensile strength and a markedresistance to tearing. Upcn tearing, it shows an unusually long white'fiber. When properly treated, it shows characteristics that make it desirable for glove leather. It possesses the unusual characteristic of being washable. Its properties can be varied over a very wide range for a great variety of uses. This leather contains upward of 0.5 part of P205 combined with 100 parts of hide substance. The P205 is combined with the hide substance in such manner as to resist removal by washing, as diiferentiated from P205 in other forms not in combination with the hide substance.

After tanning leather by the use of the previously described agents there will be present in the leather phosphates of three different types, 1) water-soluble unombined phosphate, (2) water-insoluble uncombined phosphate, (3)

.phosphate chemically combined with the hide protein. The determination of'the chemically combined phosphate should be made as follows:

A sample 'of the leather is washed in running water for 24 hours to remove all of the uncombined water-soluble phosphate. It is then subjected to the action of boiling nitric acid until completely oxidized and dissolved. This will bequire about three hours. A clear solution results. The solution is thenevaporated nearly to dryness to drive off the excess nitric acid. The mixture is then dissolved in water and ammonia is added to make the water fairly alkaline. This causes a precipitation of the phosphate originally present in the leather asuncombined and water-insoluble. The phosphate left in the solution is' that which was originally chemically combined with the hide protein. The mixture is filtered and the phosphate present in the filtrate is determined by the standard double precipitation method for deter mining phosphate, using ammonium molybdate and magnesium mixture.

An example of the amounts of P205v which may combine with the hide substance'at various pH values is given in the foregoing Table I. 'The amount of P205 which combines with the hide substance may be varied as desired, but for most purposes there will be from'about 0.5 to 8 parts or more per 100 parts of hide substance.

The amount of P205 combined may also be varied by using glassy materials of different NazO to P205 ratio at some desired pH. Table III shows the extent of combination of P205 for four glassy phosphates ranging in composition from a tanning liquor being 2.4. It is evident that the amount of combined P205 increases steadily as the ratio of NazO to P205 decreases to the 1:1 ratio of sodium metaphosphate.

Table III N 0 GI%IRS(?2QII om me Wl Ratio p 0 00 grams hide substance Although I have referred to the use of formaldehyde in the phosphate tanning liquor, I may use other aldehydes, for example, acetaldehyde or other aldehydes in place of the formaldehyde.

While I prefer to use the phosphates of sodium because of their cheapness, other alkali-metal soluble phosphates may be employed, such for example as the soluble phosphates of potassium or ammonium, or the corresponding acids in which one or more of the alkali-metal atoms are replaced by hydrogen atoms. Accordingly, in the claims the term .alkali-metal phosphate is intended to' include the corresponding acid,

I have given certain examples of the manner in which my invention may be carried out.

Many-variations in procedure may be made in order to make the product more suitable for special uses and the invention may be otherwise embodied or practiced within the scope of the following claims.

I claim:

1. A method of tanning animal skin, which comprises treating the skin with a solution containing asits essential tanning agent a-compound of the formula (M2O)2:.(P2O5)y, in which M is P205 is less than 2:1.

.3. A method of tanning animal skin, which comprises treating the skin with a solution containing as its essential tanning agent an alkalimetal salt of a phosphoric acid which ismolecularly dehydrated to a greater extent than pyrophosphoric acid.

4. A method of tanning animal skin, which comprises treating the skin with a solution containing as its essential tanning agent a sodium salt of a phosphoric acid which is molecularly dehydrated to a greater extent than pyrophosphoric acid.

5. A method of tanning animal skin, which comprises treating the skin with a solution con taining Graham's salt as its essential tanning agent.

6. A method of tanning' animal skin, which comprises treating the skin with an acid solution containing Graham's salt as its essential tanning agent.

7. A method of tanning animal skin, which comprises treating the skin with a solution 'con taining Graham's salt as its essential tanning agent, the solution being substantially free of other tanning agents.

comprises treating the skin with a solution containing Grahams salt and formaldehyde.

9. A method of tanning animal skin, which comprises treating the skin with an acid solution containing Grahams salt and formaldehyde.

10. A method of tanning animal skin, which comprises treating the skin with-an acid solution of formaldehyde and Grahamssalt, and after a. sufficient period of tanning, making the solution alkaline and continuing the tanning.

11. A method of tanning animal skin, which comprises employing as the essential tanning agent a solution of a glassy material of theformula (M20)a:.(P205)g/, in which M is-hydrogen, ammonium and/or an alkali-metal, and in which the molar ratio of M20 to P20: is less than 2:1.

12. A method of tanning animal skin, which comprises employing as the essential tanning agent an acid solution of a glassy material of the formula (M2O).1:.P2O5)y, in which M is hydrogen, ammonium and/or analkali-m'etal, and

in which the molar ratio of M20 to P205 is less than 2:1. r

13. A method of tanning animal skin, which comprises employing as the essential tanning agent a solution of the formula H2P04(HP02)2. in which a: is greater than 1.,

14. A method of tanning animal skin, which comprises employing as the essential tanning agent a solution of a condensed phosphoric acid in which the ratio of H20 to P205 is less than 2: 1.

15. A method of tanning animal skin, which comprises employing as the essential tanning agent a solution of the formula (MPO3), in which M represents an alkali-metal or ammonium and inwhich a: is greater than 3. w

16. A method of tanning animal skin, which comprises treating the skin with a solution containing an aldehyde and a glassy material of the formula (M20) z-(P205)1{, in which M is hydrogen, ammonium and/or an alkali-metal, and in which the molar ratio of M20 to P205 is less than 2:1. i

17. A method of tanning animal skin, which comprises treating the skin with an acidsolution containing analdehyde and a'glassy material of the formula (M20) 2.(P205) y, in which M .is hydrogen, ammonium and/or an alkali-metal; and in which the molar ratio of M20 to P205 is less than 2:1.

18. A tanning solution containing as its essential tanning agent a compound of the formula (M2O)a:.(P205) in which M is hydrogen, ammonium and/or an alkali-metal, and in which the molar ratio of M20 to P205 is less than 2:1. 19. An acid tanning solution containing as its essential tanning agent a compound of the formula (M2O).2.(l-205) in which M is hydrogen, ammonium and/or an alkali-metal, and in which the molar ratio of M20 tov P205 is less than 2:1.

20. A tanning solution containing as its essential tanning agent an alkali-metal salt of a phosphoric-acid which is molecularly dehydrated to a greater extent than pyrophosphoric acid. 21. A tanning solution containing as its essential tanning agent a sodium salt of a phosphoric acid which is molecularly dehydrated to a greater extent than pyrophosphoric acid.

22. A tanning liquor containing as its essential tanning agent a solution of a glassy material of the formula (M2O)z.(P2Q5)1/, in which M is hydrogen, ammonium and/or an alkali-metal, and.

in which the molar ratio of M20 to P205 is less than 2:1. 8. A' method of tanning animal skin, which 23. A tanning solution containing Graham's salt asits essential tanning agent. i

24. A'strongly acidtanning solution containing Graham's salt as its essential tanning agent.

25. A'tanning solution containing formaldehyde and Graham's salt.

26. A tanning liquor containing'as its essential tanning agent a solution of a glassy material of the formula (M20) 2.(P20.5) v, .in which M is hydrogen, ammonium and/or an alkali-metal, and in which the molar ratio of M20 to P205 is less than 2:1. i a

- 27. A tanning liquor containing as its essential tanning agent a solution of the formula H:P04(HP02), in which a: is greater than I.

28. A tanning liquor containing as its essential tanning agent a solution of a. condensed phosphoric acid in which the ratio of H20 to P205 is less than 2:1. p

29. A tanning liquor containing as its essential tanning agent a solution of the'formula (MPOs) 2,

'in whichM represents an alkali-metal or ammonium and in which-a: is greater than 3.

30. An acid tanning liquor containing as its 1 essential tanning agent a solution oi'fa glassy material 01 the formula (M20)2.(P205) in which M, is hydrogenammonium and/or an alkalimetaL-and in which the molar ratio of M20 to P205 is less than 221.

' 31. A tanning liquor containing an aldehyde and a solution of a glassy material of the formula (M20) 2.(P205) in which M is hydrogen, am-

'monium and/or an alkali-metal, and in which the molar ratio of M20 to P205 is less than 2:1. 32. A-method of tanning animal skin, which comprises treating the skin with a solution containing an aldehyde and a compound of the formula (M20)2.(P205) in which M is hydrogen,

ammonium and/or an alkali-metal, and in which the molar ratio of M20 to P205 is less than 2:1.

33. A method 01' tanning animal skin, which comprises employing as the essentialtanning agent a solution of an alkali-metal trimetaphosphate.

hide protein acquires a maximum positive electrical charge.

36. A method of tanning animal skin, which comprises treating the skin with an acid solution containing as its essential tanning agent a compound of the formula (M20)=.(P205)11, in which M is hydrogen, ammonium and/or an alkalimetal, and in which the molar ratio of M20 to P205 is less than 2:1, the pH value of the solution being approximately 2.4.

37. A method of tanning animal skin, which I comprises treating the skin with an acid solution containing as its essential tanning agent a compound of the formula (M20)=.(P20 5)v, in which,

M is hydrogen, ammonium and/or an alkalimetal, and in which the molar ratio of M20 to P205 is less than 2:1, the pH value of the solution being between approximately 2 and 4.

38. Leather containing more than one part P205 chemically combined with one hundred parts of hide substance.

39. Leather containing more than one part P205 chemically combined with one hundred parts of hide substance, the combined P205 being substimtially free from metallic tanning, agents.

40. Leather containing more than one part P205 chemically combined with one hundred parts of hide substance, the combined P205 being substantially free from other tanning agents.

41. Leather containing more than one part P205 chemically combined with one hundred parts of hide substance, the leather being substantially free from other tanning agents.

42. Leather tanned in a solution having a pH value between about 2 and 4 and containing as its essential tanning agent a compound of the formula (M20) :n-(P205')y,-1n which M is hydrogen, ammonium and/or an alkali metal, and inwhich the molar ratio of M20 to P205 is less than 2:1, the leather containing more than one part P205- chemically combined with one hundred parts of hide substance, the leather being characterized by high tensile strength, high resistance to abrasion, long fibre and by being washable without unduly afiecting its physical properties.

43. White leather, which is white entirely been tanned in a'solution having a pH value between about 2 and 4 and containing as its 

